Summary An Air Canada JazzDHC-8-300 (registrationC-GABP, serial number257), operating as FlightJAZZ8710, was proceeding from Montral, Quebec, to Qubec, Quebec, with three crew members and three passengers on board. After take-off, at about 3000feet above sea level, the aircraft banked left and force had to be applied on the steering wheel to keep the wings level. The checklist for a runaway aileron trim tab was completed, which corrected the situation. However, the flight crew found that the trim tab indication, which was fully to the right, was not normal. Emergency services were requested and the aircraft continued on its flight to Qubec. On final approach for Runway24 at Qubec, the crew was advised by the controller that the airline required it to not continue with the approach. A missed approach was executed and it was suggested to the captain that he come back for a no-flaps landing. The aircraft came back and landed with no flaps without incident at 1052 eastern standard time. Ce rapport est galement disponible en franais. Other Factual Information The flight crew was certified and qualified for the flight in accordance with existing regulations. Weather conditions were suitable for visual flight and there is no evidence that weather was a contributing factor in this occurrence. The aircraft records indicate that it was certified, equipped and maintained in accordance with existing regulations and approved procedures. The aircraft was authorized to fly in accordance with minimum equipment list (MEL)27-1 because of a defective aileron trim tab indicator. In this situation, the trim tab must be checked visually from the outside prior to each departure and a placard must be placed near the indicator. The investigation established that there was no check as required by the MEL and there was no placard in place. It could not be determined whether a placard had ever been posted or whether it fell off after a period of time. The flight crew on the previous flight had completed the MEL procedure prior to departure from Qubec. During their flight, the previous crew had no problems with the trim tab and it was not necessary to use it. The occurrence flight was the third flight of the day for the crew, but the first on aircraft C-GABP. The departure from Montral was scheduled for 1000 eastern standard time.1 Prior to departure, the first officer read the flight plan, which mentioned the defective indicator and the reference to MEL27-1. He informed the captain of it. The captain paid little attention to the reported deficiency, since those indicated in the flight plan do not always match those indicated in the aircraft logbook. The captain intended to review the deficiencies reported in the logbook after boarding the aircraft. On arriving at the aircraft, he carried out the external inspection and noted no deficiencies. However, he did not check the trim tab as required by the MEL because he had not yet read the logbook, which would have referred him to the MEL and the procedure to follow. After boarding, the crew was informed by maintenance personnel that the crew on the previous flight had reported a severe airframe vibration. The captain was surprised and concerned about the level of vibration reported. A propeller balancer was installed in the cockpit and the crew read the operating instructions for it. The maintenance personnel left the aircraft with the logbook to make the necessary entries. The logbook is made up of two documents, which are referred to as Part1 and Part2. The two parts are fastened together between plates of aluminum. Deficiencies are recorded in Part2 of the logbook. Because Part2 was full, a new Part2 was added so that the entry about the vibration could be made. The logbook therefore was made up of Part1 and two Part2s when it was returned to the captain a few minutes before departure. The captain noted the entry about the vibration but did not note the defective trim tab indicator, which was in the old Part2, underneath the new Part2. The investigation could not determine whether the trim tab had required adjustment on the pre-flight checks. However, the information received indicates that the indicator was centred prior to the take-off roll. The aircraft commenced taxiing at 0953 and took off at 0958. The first officer was at the controls and the captain was performing the tasks of the pilot not flying. The take-off was normal. When the aircraft was placed in level flight at 3000feet above sea level (asl), the first officer noted that the aircraft had a tendency to bank left and that the indicator was fully to the right. He advised the captain, who took the controls and confirmed that the aircraft tended to roll. It was agreed that the trim tab was a runaway, and the appropriate checklist was completed. Without looking at the indicator, the captain activated the trim tab to the right and pulled the circuit breaker. After the checklist was completed, the indicator was fully deflected to the right and the tendency to roll to the left had disappeared. Since the crew had control of the aircraft and the checklist did not require an immediate landing, the crew decided to continue to destination. While en route, checks made from the cockpit did not establish why such a large deflection was required. The crew concluded that the vibration reported by the previous crew resulted from a panel on the upper surface of the wing that was poorly fastened and had separated on departure from Montral, which would account for the absence of severe vibrations. The crew felt that the absence of the panel was now creating resistance, requiring that the trim tab be fully deflected. However, the aircraft was flying straight and it was not necessary to apply rudder or aileron. The captain radioed the maintenance coordinator at the flight dispatch centre to advise that he was experiencing control problems. He explained that the trim tab was fully deflected to the right in order to keep the wings level, and that he thought he had lost a panel, but he was not specific about this. At that time, the aircraft was about halfway to destination. The maintenance coordinator advised the flight dispatcher, who advised the assistant chief dispatcher and air traffic control (ATC). ATC was informed to have the emergency equipment on standby for the landing. Feeling that the situation could result in a major or catastrophic accident, the flight dispatcher initiated a categoryC emergency message through the fan-out notification system. This type of message is sent to certain members of management so they can prepare for their respective tasks in the event of a major or catastrophic accident. After receiving the emergency message that the aircraft was experiencing control problems, the director of flight operations and four other persons went to the office of the assistant chief dispatcher, which is located in the flight dispatch centre room. The flight dispatch centre room is divided into three sectors. Each sector has a flight dispatcher and a maintenance coordinator among others. The office of the assistant chief dispatcher is located at the other end of the same room. To monitor flights, the airline uses radar screens located in each sector and in the office of the assistant chief dispatcher. Therefore, it was possible to monitor the position, speed and altitude of the aircraft during the course of this occurrence. However, there is a time lag in the transmission of information, which means that the information displayed on the radar does not represent the aircraft's position in real time. Since he did not know the exact nature of the control problem, the director of flight operations asked the assistant chief dispatcher to advise the crew not to continue with the approach. More time was needed to determine how serious the problem was and provide adequate suggestions for the pilots. The assistant chief dispatcher phoned the Qubec control tower to have the information transmitted to the crew. By that time, the aircraft had commenced a visual approach for Runway24. When the crew received the message not to continue the approach, it was less than two miles from the runway threshold and about 665feet above ground level (agl). Since the aircraft was under control and configured for the landing, the crew decided to continue with the approach. Meanwhile, the flight dispatcher also was in contact with the tower in order to be kept advised of the progress of the landing. That is when the controller advised him that there was someone else from the airline, on another telephone line, who was demanding that the aircraft execute a missed approach. Questioning the assistant chief dispatcher about this, the flight dispatcher realized that, without his knowledge, the tower and the assistant chief dispatcher were in contact. That is when he was ordered to advise the crew to execute a missed approach. When this last instruction was received by the crew, the aircraft was at an altitude of approximately 65feet agl. The crew executed a missed approach, during which the aircraft descended to less than 50feet above the runway. Afterwards, the captain called the airline to request an explanation for the order to execute a missed approach. The loss of a panel reported by the captain gave the director of flight operations the impression that the aircraft may have lost an aileron. Therefore, he felt it was safer to land without flaps and at higher speed so the remaining aileron would be more effective. The aircraft came back around and made an uneventful no-flaps landing. The defective indicator had been reported for the first time on 26March2004. It was worked on in the ensuing days, during which the indicator was replaced and some electrical connections were repaired, which solved the problem but only temporarily. Some troubleshooting notes indicated that the problem with the indicator was intermittent and that it occurred only in flight. When it was malfunctioning, the indicator was fully deflected to the right, indicating that the trim tab was fully down. The trim tab on the DHC-8-300 is located on the right aileron. It can be deflected through a maximum of 40degrees, that is up 20degrees and down 20degrees. It is activated electrically by a rocker switch mounted on the centre console. After the occurrence, it was observed that the trim tab was centred. However, it was adjusted incorrectly; deflection was only 15degrees downward instead of 20degrees. In such a case, the trim tab would retain its maximum deflection capability of 40degrees. However, it is 25degrees upward and 15degrees downward. This faulty adjustment gives rise to two possible scenarios. If the potentiometer is correctly adjusted but the actuator or the push-rod is not correctly adjusted, the indicator, if it is working properly, will show the actual position of the trim tab. If the actuator or push-rod and the potentiometer are not correctly adjusted, the trim tab indicator will not show the actual position of the trim tab. The indicator will be centred while the trim tab is actually deflected five degrees upward.